Since the 1980s, [approximately equal to] 20 outbreaks of
cryptosporidiosis have been reported in health care facilities (1-9).
Thus far, to our knowledge, genotyping and subtyping tools have not been
used in the investigation of this type of outbreak (10). We used
subtyping in a molecular epidemiologic study of endemic
cryptosporidiosis to retrospectively identify an extended outbreak among
children in a hospital ward.

The Study

During September 2007-October 2009, fecal specimens were collected
from children in hospitals I (3,245 patients), II (489), and III
(2,550), in Shanghai, People's Republic of China. The children (1
month-19 years old, median 36 months) were hospitalized primarily for
nongastrointestinal illnesses. For each patient, information was
collected on age; sex; occurrence of diarrhea; and, later in the study,
ward assignment in hospital I. The study was approved by the ethics
committee of East China University of Science and Technology, Shanghai.

Cryptosporidium spp. were detected in the specimens and
differentiated by PCR and restriction fragment length polymorphism
analysis of the small subunit rRNA gene (11). C. hominis was subtyped by
sequence analysis of the 60-kDa glycoprotein gene (12). Each specimen
was analyzed at least 2x by PCR, with positive and negative controls in
each run. Prevalence rates and 95% CIs were computed; the [chi square]
test was used to test differences. Odds ratios (ORs) and 95% CIs were
calculated.

Among the 6,284 patients, 102 were positive for Cryptosporidium
spp.: 90 from hospital I (2.8%, 95% CI 2.2-3.3), 3 from hospital II
(0.6%, 95% CI 0-1.3), and 9 from hospital III (0.4%, 95% CI 0.1-0.6)
(p<0.01). Ward assignment was available for 1,592 of 3,245 patients
in hospital I. In most of the 12 wards, the infection rate was 0%-2.3%;
in ward A, it was 51.4% (p<0.01) (Table).

In hospital I, children <6 months old had a significantly higher
positive rate (8.4%, 95% CI 5.6-11.2) than older children (1.9%, 95% CI
1.4-2.4) (p<0.01; data not shown). This was mainly because of a high
infection rate among the age group in ward A (61.5%, 95% CI 36.9-86.2)
versus those in other wards (40.0%, 95% CI 19.0-61.0). No age associated
difference in infection rates was found in other wards (p = 0.80; data
not shown).

Cryptosporidiosis was more prevalent during February-July 2008
(p<0.01). Prevalence rates remained at [approximately equal to] 6% in
the monthly distribution of the 2 main C. hominis subtypes in hospital
I; however, when adequate numbers of patients were sampled, rates of
Cryptosporidium infection in ward A remained >28% in most study
months.

Six C. hominis subtypes were found at the 3 hospitals; 4 were in 73
specimens from hospital I (Table). Of those 73 specimens, 71 (97.3%)
were subtype IaA14R4 or IdA19, and they were mostly found in ward A and
unknown wards (Table). Other subtypes (IbA19G2 and IdA14) were not found
in ward A (Table). With 1 exception, subtypes in hospital I were not
found in other hospitals; subtype IaA14R4 was found in 2 patients in
hospital III. Likewise, subtypes IaA18R4 (in 1 patient in hospital II)
and IgA14 (in 1 patient in hospital III) were not found in hospital I.

Our data indicate that a cryptosporidiosis outbreak occurred among
children in ward A of hospital I. This conclusion was supported by the
following findings: the rate of Cryptosporidium-positive cases in ward A
(51.4%) was significantly higher than the overall rates in hospitals I
(2.8%), II (0.6%), and III (0.4%); less Cryptosporidium diversity was
found in ward A (only C. hominis) than in other wards/hospitals (4
Cryptosporidium spp.); only C. hominis subtypes IaA14R4 and IdA19 were
present among 38 ward A patients (vs. 6 subtypes in 12 patients in other
wards/hospitals); and a high rate (61.5%) of Cryptosporidium-positive
cases occurred in ward A among children <6 months old, an age that
usually has a low prevalence of cryptosporidiosis (13).

The source of the cryptosporidiosis outbreak is unknown. Most of
the 12 wards in hospital I were located in the main building; ward A,
the smallest ward, was in an adjacent building and was for children from
a welfare institute. Hired caregivers cared for children in ward A;
family members were the primary caregivers for patients in other wards.
Thus, poor diaper-changing and hand-washing practices by caregivers
could be responsible for the persistence of C. hominis infections in
ward A. However, the facts that most of the patients were examined for
Cryptosporidium infection only once and that many of the specimens were
not submitted immediately after patients were hospitalized prevented us
from concluding with certainty whether the infections were acquired in
the hospital or in the welfare institute. The likelihood for widespread
foodborne and waterborne transmission of cryptosporidiosis in hospital I
was small because children in ward A and other wards shared the same
source for food and drinking water. The likelihood of direct
transmission of cryptosporidiosis among ward A patients was also small
because 80% of patients were <1 year old and mostly stayed in cribs
and beds.

This cryptosporidiosis outbreak has several key features. First, it
was lengthy, lasting [greater than or equal to] 14 months (November
2007-December 2008); only limited sampling was done before November
2007; and Cryptosporidium spp. were still present in December 2008. The
longest previous outbreak was 4 months (14). Second, the number
([greater than or equal to] 38) of involved patients was high. Judged by
the low occurrence of the 2 subtypes in other wards, most of the 32
IaA14R4-and IdA19-positive patients with missing ward information were
probably also from ward A. Thus, >60 children might have been part of
the outbreak. Third, this outbreak was caused concurrently by 2 C.
hominis subtypes, of which IaA14R4, but not IdA19, was significantly
associated with diarrhea. The observed difference in virulence is
consistent with data from a community study in Peru (15), in which
subtype family Ia, of which IaA14R4 is a member, was more virulent than
Id, of which IdA19 is a member.

We retrospectively identified the outbreak by subtyping; the delay
in detection prevented us from doing a thorough investigation, and
continued sampling in the hospital and welfare institute and detailed
epidemiologic and environmental investigation became impossible after we
reported the outbreak to hospital I. Despite not knowing the source of
infections, hospital I took measures to reduce hospital-acquired
infections, including better training of caregivers and moving ward A to
a new location. Thus, study data highlight the power of molecular
epidemiologic tools in the surveillance and control of cryptosporidiosis
and the need for prompt identification and investigation of outbreaks in
health care facilities.

Acknowledgments

We thank the hospital personnel for assistance in specimen
collection.

This work was supported in part by the National Natural Science
Foundation of China (31110103901, 30928019 and 81041078); Fundamental
Research Funds for the Central Universities, China (WB0914044); open
funding projects of the State Key Laboratory of Bioreactor Engineering
and the State Key Laboratory of Veterinary Etiological Biology.

Dr Feng is a professor at the East China University of Science and
Technology. Her research interests are the molecular epidemiology,
pathogenesis, transmission, and environmental ecology of waterborne and
foodborne pathogens, such as Cryptosporidium and Giardia spp. and
microsporidia.

Address for correspondence: Yaoyu Feng, State Key Laboratory of
Bioreactor Engineering, School of Resources and Environmental
Engineering, East China University of Science and Technology, Shanghai
200237, People's Republic of China; email: yyfeng@ecust.edu.cn